1. Field of the Invention
The present invention relates to a passive optical network system and a method of transmitting a broadcasting signal in the same system, and more particularly, to a passive optical network system and a method of transmitting a broadcasting signal by amplifying the signal without a separate pump light source.
2. Description of the Related Art
Accompanying an increase in data required for high quality broadcasting and games, a demand for optical fiber data transmission has increased in subscriber networks. In particular, to simultaneously satisfy bulk multimedia data requirements and high quality broadcasting demand, hundreds of megabytes of data per second and multiple high quality broadcasting channels are transmitted to each subscriber in an optical subscriber network.
FIG. 1 is a block diagram of a conventional passive optical network system.
Referring to FIG. 1, the passive optical network system includes a central office (CO) 100, a plurality of optical network units (ONUs) 120, and a remote node (RN) 110, which connects the CO 100 to each of the plurality of ONUs 120, distributes optical data signals and broadcasting signals, and multiplexes upstream optical signals. The CO 100, the plurality of ONUs 120, and the RN 110 are connected to each other via optical cables 130 and 132.
The CO 100 includes a transmitter for broadcast (TXBC) 102 for generating a broadcasting signal, an optical amplifier 104 for compensating for a transmission loss in an optical transmission line when transmission is performed, an optical transceiver for data (OTRXdata) 106 generating data signals and receiving data signals from the plurality of ONUs 120, and a wavelength multiplexer (MUX) 108 for multiplexing the broadcasting signal and the data signal.
The RN 110 distributes a downstream data signal and a broadcasting signal received from the CO 100 via the optical cable 130 to each of the plurality of ONUs 120 and transmits upstream data signals received from the plurality of ONUs 120 to the CO 100 by multiplexing the upstream data signals.
Each ONU 120 includes a wavelength multiplexer/demultiplexer (MUX/DEMUX) 122 for demultiplexing the downstream data signal and the broadcasting signal transmitted from the CO 100 via the RN 110, a receiver for broadcast (RXBC) 126 for receiving the broadcasting signal, and an optical transceiver for data (OTRXdata) 124 for receiving the downstream data signal and transmitting an upstream data signal.
This scheme is detailed in a research paper entitled “Operational demonstration and filter alignment study of multiple broadcast video delivery on a WDM passive optical network”, IEEE Photonics Technology Letters, Vol. 10, No. 9, pp 1331-1333, September 1998.
In the conventional passive optical network system illustrated in FIG. 1, the optical amplifier 104 for compensating for a transmission loss of a broadcasting signal is used in the CO 100. However the optical amplifier 104 is very expensive, and since the optical amplifier 104 is configured using various parts, its configuration is complicated, resulting in a complicated system configuration.
A research paper and a patent detailing a structure of amplifying a broadcasting signal in a low price passive optical network by using only a gain medium without using an optical amplifier in order to solve the problem are outlined as follows:
In the research paper entitled “Bidirectional transmission scheme using intensity modulation of 1.48 μm pump laser diode for erbium-doped fiber amplifier”, Electronics Letters 3rd, Vol. 27, No. 1, pp 89-91, 1991, a scheme of using a data light source having a wavelength of 1.48 μm, using a signal obtained by 5 MHz phase modulating the wavelength as an optical data signal by transmitting the obtained signal to ONUs, and simultaneously using the obtained signal as a pump light source of a broadcasting signal in a gain medium is suggested. However, in this case, since the data light source is phase-modulated, a data transmission rating is low in actual use, and since a phase modulator is included, the system configuration is complicated, resulting in a cost increase of a data transmitter.
The U.S. patent entitled “Passive Optical Network System providing simultaneously both broadcasting service and data service”, US2004/0131358 A1 suggests a scheme of amplifying a broadcasting signal using a gain medium of an RN by transmitting a pump light source with a data signal and the broadcasting signal in a CO. However, in this case, since a pump light source is used, costs increase.